In the field of crystal oscillator devices, a matter of great importance is to accurately sense the temperature of the quartz resonator to perform either measurement, e.g., thermometry, or compensation and control for the purpose of frequency stabilization against variations in temperature.
In thermometry, conventional methods of sensing on the change in resistivity of the material or use electromechanical devices such as thermometric cut quartz resonators, whose operation depend on a change of resonant frequency. The latter mentioned resonator devices allow the measurement of temperature with exceptionally high accuracy and resolution. The possibility of accomplishing the same measurement, yet while requiring only a resonator manufactured without precision control over its angle of cut unlike the above mentioned resonators, would clearly be most useful.
Conventional methods for frequency stabilization by means of compensation and control rely on external temperature sensors such as described above and are inefficient in indicating the actual and instantaneous temperature of the quartz resonator to be compensated or controlled for frequency variation under varying conditions. One suggested method of resonator self temperature sensing, i.e. not employing an external temperature sensor is to use the B mode signal of a typical SC-cut crystal to secure temperature and to effect compensation and control over the C mode signal. It seems, however, that the B mode is not reliable for temperature sensing applications in currently designed resonators because of excessive and uncontrollable activity dips resulting from readily coupled undesired modes. The B mode also experiences difficulty in accurately sensing the C mode temperature because of the B mode's excessive hysteresis, i.e. thermal nonrepeatability, and inadequate thermal transient performance.
A thermometry method of utilizing a quartz resonator temperature sensor not having a special precision thermometric cut, thereby permitting use of general utility crystal cuts of the thickness shear variety and a frequency stabilization method of utilizing other than the usual B and C modes of a doubly rotated cut for this purpose, and in addition of having a reliable and accurate means of self temperature sensing is of course highly desirable.